Electric gas-discharge tube for photographic sound recording



March 9 1926. 1,575,701

H. G. MATTHEWS ELECTRIC GAS DISCHARGE TUBE FOR PHOTCGRAPHIC SOUNDRECORDING- Fied July 10, 1923 Patented Mar. 9, 1926.

UNITED STATES v 1,575,101 PATENT OFFICE.

HARRY GRINDELL MATTHEWS, OE'LONDON, ENGLAND.

ELECTRIC GAS-DISCHARGE TUBE FOR PHOTOGRAPHIG SOUND RECORDING.

Application filed iuly 10, 1923. Serial No. 650,690.

charge tubes, to be employed more especiallyv as a source ofsound-varied light for use in effecting a record on a sensitive film orother light-sensitive surface, but capable of other applications.

discharge tube is employed as a source of actinic light, varied by thecircuit of a microphone or other electrical soundrecep tor.

An advantage accruing from the use of a gas discharge tube as comparedwith other electrical sources of light, is the smallness of thesound-varied current suflicing to vary the light, thus avoiding any.tendency for the microphone or the like to burn out.

.The ob ect, of the present invention is to provide the light emittingelectrode of a gas discharge tube employed as avaried source of light,with an elongated light-emitting surface of an area considerablygreater. than the sectional area of the beam of light emitted thereby,such that the superposed effect of points of light emission areconcentrated in the beam.

For this purpose, according to the invention, the surface of the lightemitting electrode (cathode) of the gas discharge tube is formed with adeep longitudinal groove.

By a deep groove is meant one of which the depthis'several times thewidth of the mouth of the groove I lVith-a suitably located anode andwith a suitable pressure of gas in the tube,,the glow of light will belocated within the groove ofthe cathode.

The efi'ectof-the groove in the cathode is not only to concentrate thelight emitting surface but results in an increasedyvariation of thelight when influenced by soundvaried currents. Such increased variationmoreover being localized, is therefore-constantly positioned for'actingon a light sensitive surface through a small slot.

.An example of a gas discharge tube ac:

cording to the invention and a representat1ve diagram of the connectionssuitable for employing such a tube for photo-graphically recording soundon a travelling sensitivefilm, are illustrated on the accompanying-drawing, in which Fig. 1 is a sectional plan of one form of gasdischarge tube, and

Fig. 2 is a transverse section thereof.

Fig. 3 is a diagram of-the electrical connections of the tube with amicrophone.

Referring to Figs. 1 and 2, an electrode a of a gas discharge tube a isformed with a deep longitudinal groove 6, by the electrode a consistingof a sheet of metal folded For recording purposes, an electric gas aboutits middle and with outwardly turned borders, see Fig. 2.

The other electrode consists of a. 0 with a hole d opposite the groovethe first electrode a and adjacent to the outwardly turned bordersthereof.

The electrode a is'the cathode and electrode 0 is the anode.

As shown in Fig. 1, the groove '6 of the electrode a is arrangedopposite and parallel to a gate 0 behind which passes a travelling.light-sensitive film f, 50 that variations in the light emitted from theelectrode a, with in the groove 6, effect a varying: photo graphicrecord on the film f.

the i In the illustrated example, the film f istowards the film f, lightfrom a surface of greater area thanrthe area of the beam of In therepresentativediagram of electrical connections shown in ,Fig. 3, thetube a -is connected to an energizing battery of-250- 300- volts 9through" a --graphite segment potentiometer h, with'the secondary i of alow frequency transformer a in parallel with the tube a j is avoltameter in shunt across the terminals of the tubea and his amicroammeter in series with the tube. Z is a telephone in series withthe secondary Z of an. air core. transformer, the primary Z of which isin serieswith-the'tube m for en abling audible observation 'of the.battery' and tube circuit. The telephone Z may, howlight acts upon thefilm and thereforeintem 'SlfiGS the photographic efiect and exaggeratesthe variations thereof.

ever, be directly connected in the battery and tube circuit. is thebattery switch, 9 is a fixed condenser for preventing dlscharge of thebattery 9 through the primary winding i and g is a choking coll forpreventing the pulsations from the transformer '11 assmg through thebattery circuit.

he primary i of the transformer i is connected in series with the platecircuit of a pair of thermionic valves m in parallel, the grid circuitof which is connected in series with the secondary n of a low frequencytransformer 71.. 0 is the hlgh tension battery and p the low tensionfilament battery of the valves m.

The primary n of the transformer 11. is connected in series with theplate circuit of a thermionic valve g, the grid circuit of which isconnected to the secondary r of a low frequency transformer r. s is thehigh tension battery and t the low tension battery of the valve 9.

The primary 7' of the transformer 1' is in series with a battery u ofabout 4% volts, in the circuit of which is a microphone 'v, or aplurality of microphones variously connected, i. e. in series, parallelor seriesparallel.

I claim:

In an electric gas discharge tube, a light emitting cathode consistingof a sheet of metal folded about its middle with outwardly turnedborders, and an anode consisting of a plate with a hole opposite saidfolded portion of said sheet and adjacent said outwardly turned bordersthereof.

In testimony whereof I have signed my name to this specification.

HARRY GRINDELL MATTHEWS.

